1. Field of the Invention
This invention relates to conduits as used for conveying flowable material and, more particularly, to a system for controlling elongation of such conduits under the weight of the conduit and contained material, together with the weight of any pumps, or the like, attached thereto, and supply lines for powering the pumps.
2. Background Art
Conduits are used to convey flowable materials in many different environments, and for many different applications. As one example, it is known to attach a submersible pump to the end of a conduit and to direct the pump downwardly into a well as to recover water, oil, or the like.
In certain operations, the pump will be directed downwardly into a bore or well with a depth in excess of 1,000 feet. The upper regions of the conduit are thus subjected to weight forces that are substantial, including those of the pump, the conduit, the material contained in the conduit, and power supply lines for the pump. With the conduit made from a non-metal material, these forces may cause significant elongation of the conduit, and in a worse case, failure thereof.
Typically, hoses designed for this application are braided high pressure hoses, much like thermoplastic hydraulic hoses consisting of an extruded inner core tube, one or more braids of high tensile yarns, and an extruded jacket providing abrasion and chemical resistance.
Elongation of this type of hose may cause an appreciable reduction of the cross-sectional area of the flow passageway defined thereby. This limits flow capacity and, as a result, pumping efficiency.
This elongation may be to a certain extent limited by metal, conductive wires that supply power to the pump. However, such wires may not be designed to bear the encountered weight forces, as a result of which there is a risk that the power supply to the pump may be compromised.
The above elongation problem may be aggravated by elevated temperatures at the bottom region of the well/bore, that make the conduit material even more extensible.
Attempts to reconstruct the conduit to limit detrimental elongation may introduce other problems. The tensile strength of the inner core tube and covering layers/materials is directly related to the flexural modulus for the materials from which they are constructed. To provide appreciable resistance to stretching/elongation, very stiff materials may have to be used, as a result of which the conduits become stiff and difficult to handle. This is particularly a problem where a substantial length of conduit is required and in which situations the conduit would normally be stored upon, and paid off of, a storage reel. Thus, the goals of facilitating handling and limiting elongation compete with each other.
To avoid the problems associated with conduit elongation, it is also known to provide a lifting cable that is attached to a pump and extends continuously to above ground, from where the cable can be selectively drawn upwardly and lowered to control the vertical positioning of the pump. With this system, the lifting cable itself becomes a component, separate from the conduit, that must be stored and handled by an operator. Aside from the inconvenience associated with this design, the externally located cable may have a tendency to become tangled as the pump is raised and lowered during a procedure. This latter problem becomes even more significant in applications wherein forces applied to the conduit are not substantially vertical, whereupon the cable may become slackened and may coil or otherwise reconfigure towards a set shape that interferes with its handling.
It is further known to vary the cross-section of such conduits to allow integration of components that are less susceptible to elongation. With this design, both the weight and the cost of the conduit may be significantly increased.
As an alternative to using conduits made from thermoplastic material, metal/steel conduits can be used. Currently, metal conduit is made with a maximum of 33 foot lengths. The lengths have threaded ends that are selectively joinable, one to the next, to produce a combined, required length. This is an inconvenient and time consuming process, both in terms of the initial setup and removal of the system at the completion of a project. Even if the system is designed to be left in place after a project, any maintenance or repair that is carried out will require the sequential disconnection of the conduit lengths as the pump is elevated and accessed. Once the repair/maintenance is carried out, re-installation through the same process must be effected.
The use of a single length of conduit made from a flexible material obviates the above problems and allows the conduit to be conveniently retrieved upon, and paid off of, a storage spool. However, as noted above, if the conduit with this construction is rigid in nature, it is difficult to handle. If the conduit is flexible in nature, it is prone to the aforementioned elongation that may create operational problems, as described above.
The above, and other, problems have been contended with in the industry since there have not been developed designs that adequately and practically address those problems.